Abstract
Germination of lettuce (Lactuca sativa L. cv. Grand Rapids) seeds is regulated by phytochrome, which is mediated by gibberellin (GA). We have shown that expression levels of LsGA3ox1 increased and those of LsGA2ox2 decreased after red-light irradiation, resulting in an increase in the levels of physiologically active GA, GA_1,during germination of lettuce seeds. It has been reported that application of abscisic acid (ABA) suppresses germination of the lettuce seeds treated with red light or GA. In this study, to investigate the mechanism for the suppression of germination by application of ABA, we analyzed expression patterns of genes encoding GA biosynthesis and deactivation enzymes in imbibed seeds irradiated with far-red light or red light. Quantitative RT-PCR analysis showed that transcript levels of LsGA3ox1 decreased, whereas those of LsGA2ox2 increased, by ABA treatment. Transcript levels of other GA-related genes that we examined were not altered by ABA under both light conditions. These results suggested that application of ABA affected GA biosynthesis and catabolism genes, of which expression is regulated by phytochrome. Such changes in transcript levels might result in the suppression of the increase in GA_1 content even in red-light-treated seeds.
